The invention provides a paraffin removal and viscosity reduction device for an oil well to provide an underground electric heating device which is good in energy-saving effect, paraffin removal function and viscosity reduction function. The device is characterized in that the device is composed of a transformer, an electric heating body, a sensor, a programmable controller, an optical fiber temperature measuring module, a middle relay, a transformer gear switching contactor, a power adjusting module, a pithead temperature transmitter, an analog quantity I/O expansion module, a control circuit and a power supply circuit, wherein the transformer has multiple voltage output gears, and the control circuit and the power supply circuit are matched with the electric heating body; the pithead temperature transmitter inputs an acquired pithead temperature signal to the programmable controller; the programmable controller controls an output gear of the transformer and the output power of the power adjusting module; work voltage is provided for the electric heating body through the transformer, and the output power of the electric heating body is controlled by the power adjusting module; the sensor is an optical fiber, and the sensor is connected with the optical fiber temperature measuring module through an optical fiber access port to provide underground temperature data for the optical fiber temperature measuring module.